At a recent Colorado rally, country singer Jo Dee Messina crooned to the crowd. To pump them up another notch, she led a rendition of “Happy Birthday” dedicated to Fox News’ Carl Cameron, a darling among conservative voters. Mike Rowe of “Dirty Jobs” came to Ohio equipped with roadkill anecdotes. And based on the “woo-ing” voters, the mere presence of golf legend Jack Nicklaus seemed to do the trick.

There’s an art to creating enthusiasm at campaign events, Romney staffers have said. Sometimes it’s a high school band. Sometimes it’s a foam hand shaped like a “Mitt.” Lately, though, it’s been a string of celebrities…